Compact annular field imager and method for imaging electromagnetic radiation

ABSTRACT

The present disclosure provides an optical imager and a method for imaging electromagnetic radiation. In one aspect, the optical imager includes an object array substantially located at an object plane, a first catadioptric element configured to substantially collimate, at a central plane, electromagnetic radiation emanating from the object array, a second catadioptric element configured to image the substantially collimated electromagnetic radiation from the central plane onto an image plane, and a detecting element substantially located at the image plane. The first catadioptric element includes at least one refractive surface and at least one reflective surface, and the second catadioptric element includes at least one refractive surface and at least one reflective surface.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Application No.61/783,507, filed on Mar. 14, 2013, which is incorporated by referenceherein in its entirety and for all purposes.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with U.S. Government support from the U.S. Armyunder contract W31P4Q-09-D-0004. The U.S. Government has certain rightsin the invention.

BACKGROUND

The present disclosure relates generally to an imaging relay lens systemand a method for imaging electromagnetic radiation. More particularly,the present disclosure relates to an imaging relay lens system having acompact configuration and a method for imaging electromagneticradiation.

The term “object array” can refer to any number of devices, such as butnot limited to a fiber array, VCSEL array, detector array, or otherobject plane, and is hereinafter referred to generally as the objectarray. The term “image array” can refer to any number of sources, suchas but not limited to a fiber array, VCSEL array, detector array, orother image plane, and is hereinafter referred to generally as the imagearray.

Reference is made to FIG. 1A, which illustrates an imaging relay lens100 made up of a pair of gradient index (GRIN) lenses 10 and 20 used toimage or reimage (hereinafter referred to generally as “image”) anobject array 30 to an image array 40. Reference is also made to FIG. 1B,which illustrates an imaging relay lens 200 comprising a pair ofaspheric lenses 210 and 220 used to image an object array 30 to an imagearray 40. See, for example, U.S. Pat. Nos. 6,635,861, 7,015,454, and7,446,298, which are incorporated herein by reference in their entiretyand for all purposes.

The distance between object array 30 and image array 40 in these designscan be significantly long compared to the size of the array. While suchdistances may be acceptable for fiber coupling connectors and othersimilar devices, they are typically too long for other applications,such as but not limited to the board-to-board optical communicationapplications, which have much shorter separations. A view of an objectarray 30 and image array 40 for these configurations, taken along aplane perpendicular to optical axis 50, are shown next to theirrespective arrays in FIG. 1A and FIG. 1B.

Accordingly, there is a need to develop a new imaging relay lens systemwith a compact configuration.

SUMMARY

Characteristics of the present disclosure are to provide an imaging lensdesign that is compact in physical size.

Further characteristics of the present disclosure are to provide animaging lens design that has a high image quality.

Further characteristics of the present disclosure are to provide anImaging lens design that has a high degree of alignment tolerance.

Further characteristics of the present disclosure are to provide animaging lens design that has a combination of the characteristicsdescribed above with superior trade-offs than have been previouslyattainable.

In accordance with an aspect, the present disclosure provides an opticalimager comprising an object array substantially located at an objectplane, a first catadioptric element configured to substantiallycollimate, at a central plane, electromagnetic radiation emanating fromthe object array, wherein the first catadioptric element comprises atleast one refractive surface and at least one reflective surface, asecond catadioptric element configured to image the substantiallycollimated electromagnetic radiation from the central plane onto animage plane, wherein the second catadioptric element comprises at leastone refractive surface and at least one reflective surface, and adetecting element substantially located at the image plane.

In one embodiment, the first catadioptric element comprises a concavesurface and a convex surface opposing the concave surface. In oneembodiment, the concave surface comprises a first refractive surface anda second reflective surface, and the first refractive surface of theconcave surface has a ring shape surrounding the second reflectivesurface of the concave surface. In one embodiment, the convex surfacecomprises a first reflective surface and a second refractive surface,and the first reflective surface of the convex surface has a ring shapesurrounding the second refractive surface of the convex surface.

In one embodiment, the object array comprises a plurality of lightemanating elements arranged in an annular region of the object array,the light emanating elements emanating the electromagnetic radiation.The at least one refractive surface of the first catadioptric element isaligned with the light emanating elements to receive the electromagneticradiation. In one embodiment, the light emanating elements are arrangedto constitute one or more concentric rings, and the light emanatingelements in one of the concentric rings are located to have asubstantially equal distance from an optical axis of the optical imager.In one embodiment, the first catadioptric element is orientedsubstantially symmetric to the second catadioptric element about acentral plane.

In accordance with an aspect, the present disclosure provides a methodfor imaging electromagnetic radiation. The method comprisessubstantially collimating, through a first catadioptric element,electromagnetic radiation emanating from at least one source elementlocated substantially at an object plane, the first catadioptric elementcomprising at least one refractive surface and at least one reflectivesurface; imaging, through a second catadioptric element, thesubstantially collimated electromagnetic radiation onto at least onedetecting element located substantially at an image plane, the secondcatadioptric element comprising at least one refractive surface and atleast one reflective surface; and detecting the electromagneticradiation

For a better understanding of the present disclosure, together withother and further characteristics thereof, reference is made to theaccompanying drawings and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B illustrate schematic views of conventional imaging relaylenses, taken along their respective optical axes;

FIG. 2 illustrates a scaled schematic view of a compact imaging relaylens with high image quality, taken along its optical axis, inaccordance with an embodiment of the present disclosure;

FIG. 3 illustrates a schematic comparison of the imaging relay lensesshown in FIGS. 1A and 1B, and the compact imaging relay lens shown inFIG. 2;

FIG. 4 illustrates a schematic view of the compact imaging relay lens ofFIG. 2, including an exemplary optical ray trace;

FIG. 5 illustrates a schematic view of an object array of the compactimaging relay lens shown in FIG. 2, taken along a plane perpendicular toan optical axis, in accordance with an embodiment of the presentdisclosure; and

FIG. 6 illustrates lateral and isometric views of a half relay lenscomponent of the compact imaging relay lens as shown FIG. 2, inaccordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

Referring to FIG. 2, there is illustrated a schematic view of a compactimaging relay lens 300, taken along its optical axis 350, in accordancewith an embodiment of the present disclosure. In one embodiment, compactimaging relay lens 300 includes a pair of half relay lenses 310 and 320,each comprising a catadioptric element, to image an object array 330 toan image array 340. In some embodiments, image array 340 can be a CCDarray, phosphorescent screen, photographic film, microbolometer array,or other means of detecting light energy.

Many optical imaging aberrations have spatial field dependencies, suchthat the image quality for elements of object array 330 are often imagedwith varying aberrations, making it difficult to image object array 330with large numbers of elements. FIG. 2 also illustrates a view ofannular field object array 330 and image array 340, taken along a planeperpendicular to optical axis 350, next to their respective relay lenses310 and 320. Although two relay lenses 310 and 320 are shown anddescribed in the present disclosure, it is appreciated that compactimaging relay lens 300 may be configured to include a single relay lens.

By restricting object array 330 substantially to an annular field 332,where a plurality of elements 334 of object array 330 are substantiallylocated to have a substantially equal distance from optical axis 350,elements 334 of object array 330 can be imaged by the pair of half relaylenses 310 and 320 with substantially the same aberration content. FIG.2 shows an exemplary arrangement of elements 334, which includes twoconcentric rings of circular elements 334. Therefore, half relay lens310 can be better corrected over annular field 332 than the conventionalapproaches where the aberration correction is typically required overthe entire spatial field from optical axis 350 to the element with thefurthest distance from optical axis 350. This reduced aberration contentcan also provide increased image quality over conventional imaging relaylens designs. In some embodiments, elements 334 of object array 330 maybe apertures of an opaque substrate, thereby allowing electromagneticradiation or light to pass therethrough, or point light sources, such aslight emitting diodes (LED), quantum dots, and the like.

Because object array 330 is restricted to substantially to an annularfield 332, in this embodiment, image array 340 is also substantiallyrestricted to an annular field 342, where a plurality of detectingelements 344 of image array 340 are substantially located to have asubstantially equal distance from optical axis 350. FIG. 2 shows anexemplary arrangement of detecting elements 344, which includes twoconcentric rings of photodetectors 344.

FIG. 3 illustrates a scaled schematic comparison of the imaging relaylenses 100 and 200 shown in FIGS. 1A and 1B, and the compact imagingrelay lens 300 shown in FIG. 2. As shown in FIG. 3, the size of compactrelay lens 300 is much smaller than that of imaging relay lenses 100 and200. Particularly, the linear distance between object array 330 andimage array 340 of imaging relay lens 300 is much shorter than thelinear distance between object array 30 and image array 40 of imagingrelay lenses 100 and 200.

FIG. 4 illustrates a schematic view of compact imaging relay lens 300 ofFIG. 2, including an optical ray trace for a single object element 334within annular field 332. In this embodiment, light originating from anelement 334 of object array 330 is incident upon first half relay lens310 comprising a catadioptric element.

Referring to FIG. 4, the light is refracted by a first optical surface312, which is capable of substantially receiving the light. The light isthen substantially transmitted to a first reflective surface 314, whichis capable of substantially receiving the light refracted by firstoptical surface 312. The light is then reflected by first reflectivesurface 314 and transmitted to a second reflective surface 316, which iscapable of substantially receiving the light reflected by firstreflective surface 314. The light is then reflected by second reflectivesurface 316 and transmitted to a second optical surface 318, which iscapable of substantially receiving the light reflected by secondreflective surface 316. The light is then refracted by second opticalsurface 318 and transmitted towards a second half relay lens 320, whichis oriented in a manner substantially symmetric to first half relay lens310 about a central plane 380 separating the two lenses 310 and 320.

Referring still to FIG. 4, the light is further incident upon secondhalf relay lens 320 comprising a catadioptric element. The light isrefracted by a first optical surface 322, which is capable ofsubstantially receiving the light, and substantially transmitted to afirst reflective surface 324, which is capable of substantiallyreceiving the light refracted by first optical surface 322. The light isthen reflected by first reflective surface 324 and transmitted to asecond reflective surface 326, which is capable of substantiallyreceiving the light reflected by first reflective surface 324. The lightis then reflected by second reflective surface 326 and transmitted to asecond optical surface 328, which is capable of substantially receivingthe light reflected by second reflective surface 326, where the light isrefracted and imaged to image array 340. It is appreciated that, inpractice, the half relay lenses 310 and 320 can include any combinationof refractive, reflective, or catadioptric elements.

FIG. 5 illustrates a schematic view of an object array 330 of compactimaging relay lens 300 shown in FIG. 2, taken along a planeperpendicular to optical axis 350, in accordance with an embodiment ofthe present disclosure. As shown in FIG. 5, annular field 332 ofelements 334 in object array 330 includes two concentric rings ofcircular elements 334. It is appreciated that, in practice, these arrayscan include any number of rings or annular configuration of elementswith various shapes and sizes.

FIG. 6 illustrates lateral and isometric views of half relay lenscomponent 310 of compact imaging relay lens 300 as shown FIG. 2, inaccordance with an embodiment of the present disclosure. As shown inFIG. 6, half relay lens component 310 includes reflective and refractivesurfaces 312, 314, 316, and 318. In this embodiment, a concave surfaceS1 includes first refractive surface 312 and second reflective surface316, while a convex surface S2 includes first reflective surface 314 andsecond refractive surface 318. In some embodiments, first and secondreflective surfaces 314 and 316 may be formed by coating one or morelayers of reflective material (e.g., metal layer or dielectricmultilayers) on half relay lens component 310.

The compact annular field imager of the present invention has beenhereto shown as operating in pairs as an optical relay lens, whichinherently provides natural correction of odd-order aberration withinthe optical system. However, these annular field imagers can also beused independently as infinite conjugate annular field imagers to imagean annular field of object points in a given scene onto an image array.

As used herein, the singular forms “a,” “an,” and “the” include theplural reference unless the context clearly dictates otherwise. Exceptwhere otherwise indicated, all numbers expressing quantities ofingredients, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about.”

For the purpose of better describing and defining the present invention,it is noted that terms of degree (e.g., “substantially,” “about,” andthe like) may be used in the specification and/or in the claims. Suchterms of degree are utilized herein to represent the inherent degree ofuncertainty that may be attributed to any quantitative comparison,value, measurement, and/or other representation. The terms of degree mayalso be utilized herein to represent the degree by which a quantitativerepresentation may vary (e.g., ±10%) from a stated reference withoutresulting in a change in the basic function of the subject matter atissue.

Although embodiments of the present teachings have been described indetail, it is to be understood that such embodiments are described forexemplary and illustrative purposes only. Various changes and/ormodifications may be made by those skilled in the relevant art withoutdeparting from the spirit and scope of the present disclosure as definedin the appended claims.

What is claimed is:
 1. An optical imager, comprising; a firstcatadioptric element configured to substantially collimate, at a centralplane, electromagnetic radiation emanating from an object array, theobject array being substantially located at an object plane; wherein thefirst catadioptric element comprises at least one refractive surface andat least one reflective surface; a second catadioptric elementconfigured to image the substantially collimated electromagneticradiation from the central plane onto an image plane, wherein the secondcatadioptric element comprises at least one refractive surface and atleast one reflective surface; and an image array substantially locatedat the image plane.
 2. The optical imager of claim 1, wherein the firstcatadioptric element comprises a concave surface and a convex surfaceopposing the concave surface.
 3. The optical imager of claim 2, whereinthe concave surface comprises a first refractive surface and a secondreflective surface.
 4. The optical imager of claim 3, wherein the firstrefractive surface of the concave surface has a ring shape surroundingthe second reflective surface of the concave surface.
 5. The opticalimager of claim 2, wherein the convex surface comprises a firstreflective surface and a second refractive surface.
 6. The opticalimager of claim 5, wherein the first reflective surface of the convexsurface has a ring shape surrounding the second refractive surface ofthe convex surface.
 7. The optical imager of claim 1, wherein the objectarray comprises a plurality of light emanating elements arranged in anannular region of the object array, said light emanating elementsemanating the electromagnetic radiation.
 8. The optical imager of claim7, wherein said at least one refractive surface of the firstcatadioptric element is aligned with the light emanating elements toreceive the electromagnetic radiation.
 9. The optical imager of claim 7,wherein the light emanating elements are arranged to constitute one ormore concentric rings.
 10. The optical imager of claim 9, wherein thelight emanating elements in one of said one or more concentric rings arelocated to have a substantially equal distance from an optical axis ofthe optical imager.
 11. The optical imager of claim 1, wherein the firstcatadioptric element is oriented substantially symmetric to the secondcatadioptric element about the central plane.
 12. An imaging relay lenssystem, comprising: a first optical system comprising at least one firstcatadioptric optical element, the first catadioptric optical elementcomprising at least one refractive surface and at least one reflectivesurface, wherein the first optical system is configured to substantiallycollimate, at a central plane, electromagnetic radiation emanating fromat least one object element; said at least one object element beinglocated substantially at an object plane; a second optical system havingat least one second catadioptric optical element, the secondcatadioptric optical element comprising at least one refractive surfaceand at least one reflective surface, wherein the second optical systemis configured to image the substantially collimated electromagneticradiation from the central plane onto an image plane; and at least onedetector element located substantially at the image plane.
 13. The lenssystem of claim 12, wherein the first catadioptric element comprises aconcave surface and a convex surface opposing the concave surface. 14.The lens system of claim 13, wherein the concave surface comprises afirst refractive surface and a second reflective surface.
 15. The lenssystem of claim 14, wherein the first refractive surface of the concavesurface has a ring shape surrounding the second reflective surface ofthe concave surface.
 16. The lens system of claim 13, wherein the convexsurface comprises a first reflective surface and a second refractivesurface.
 17. The lens system of claim 16, wherein the first reflectivesurface of the convex surface has a ring shape surrounding the secondrefractive surface of the convex surface.
 18. The lens system of claim12, wherein said at least one refractive surface of the firstcatadioptric element is aligned with said at least one object element toreceive the electromagnetic radiation.
 19. The lens system of claim 12,wherein the first catadioptric optical element is oriented substantiallysymmetric to the second catadioptric optical element about the centralplane.
 20. A method for imaging electromagnetic radiation, the methodcomprising: substantially collimating, through a first catadioptricelement, electromagnetic radiation emanating from at least one sourceelement located substantially at an object plane, the first catadioptricelement comprising at least one refractive surface and at least onereflective surface; imaging, through a second catadioptric element, thesubstantially collimated electromagnetic radiation onto at least onedetecting element located substantially at an image plane, the secondcatadioptric element comprising at least one refractive surface and atleast one reflective surface; and detecting the electromagneticradiation.